1. Field of the Invention
The present invention relates to a magnetic refrigerating material and a magnetic refrigerating device.
2. Description of the Related Art
A magnetic refrigeration technique raises expectations for refrigeration technology in view of environmental enhancement because the magnetic refrigeration technique can exhibit the high refrigeration efficiency under low energy consumption and clean environment. In this point of view, such a device as utilizing magnetic refrigeration technique within an ordinary temperature range and such a material as exhibiting a large magnetic entropy change within or in the vicinity of the ordinary temperature range are developed. An AMR (Active Magnetic Regeneration Refrigeration) method is proposed as one of promising refrigerating methods. Then, a LaFe13-based magnetic material such as La(Fe, Si)13 is proposed as one of promising refrigeration material because the LaFe13-based magnetic material can exhibit the larger magnetic entropy change, contains elemental Fe not expensive and is unlikely to cause a temperature hysteresis within the magnetic phase transition. Herein, no temperature hysteresis with the magnetic phase transition means that the magnetic condition of the material is not changed by the temperature change hysteresis.
In a magnetic refrigerating device using such a magnetic refrigeration material as described above, the intended refrigerating operation is carried out by using the magnetocaloric effect of the magnetic refrigeration material. In the case of the use of a ferromagnetic refrigeration material, for example, the intended refrigerating operation is carried out using the entropy change of the refrigeration material when the electromagnetic state is shifted from the paramagnetic state to the ferromagnetic state by the application of an external magnetic field under the condition that the refrigeration material is heated within or in the vicinity of the ferromagnetic phase transition temperature (Curie temperature; Tc).
Among the LaFe13-based magnetic material, it is known that La(Fe, Si)13 with NaZn13 type crystal structure can exhibit a relatively large magnetic entropy change. In the La (Fe, Si)13, the elemental Fe is mainly positioned at the Zn sites and the elemental La and the like are mainly positioned at the Na sites.
In order to apply the LaFe13-based magnetic material to the magnetic refrigeration using the AMR method, it is required that the LaFe13-based magnetic material is processed in small pieces such as particles in view of practical use. For example, the LaFe13-based magnetic material is crashed and processed in small pieces after thermal treatment. In this case, however, some cracks may occur in the small pieces due to the stress at the crashing so that the small pieces may become brittle. Therefore, when the brittle small pieces of the LaFe13-based magnetic material are charged into the heat exchanger of a magnetic refrigerating device so as to conduct the magnetic refrigeration through the thermal exchange between the small pieces and a coolant, the brittle small pieces may be vibrated in response to the flow of the coolant and the frequency of the application of a magnetic field for causing the thermal exchange.
If the brittle small pieces of the LaFe13-based magnetic material are vibrated for a long period of time, the small pieces are crashed and frictioned with one another, resulting in containing some cracks and being worn. In this case, the thus obtained micro particles may increase the pressure loss of the coolant and decrease the refrigeration performance.
[Reference 1] JP-A 2003-96547 (KOKAI)